** Length?** The more powder you have to burn, the more barrel length you need to burn it in. For small-capacity cases such as the .257 Roberts, .308, 7mm/08, 6.5x55, etc., you can get by quite nicely with a 20-inch barrel, although a 22-inch tube is maybe a little better. For the .270, .30/06, and other standard long cartridges, 22 inches is best, whereas 24 inches is the way to go with the standard magnums, including shortfat magnums. For varmint rifles, 26 inches is fine.